The plan was to create 2,500 miles of tunnels, covering an area of 52,000 square miles

Footage shows soldiers surveying the site before construction workers move in to begin work on the colossal subterranean structure.

The narrator explains: “Camp Century is buried below the surface of this ice cap. Beneath it, the ice descends for 6,000 feet.

“In this remote setting, less than 800 miles from the North Pole, Camp Century is a symbol of man’s unceasing goal to conquer his environment, to increase his ability to live and fight if necessary under polar conditions.

“This is the story of Camp Century: the city under ice.”

Codenamed Project Iceworm, the plan was to store hundreds of ballistic missiles beneath the frozen surface which could be launched to strike targets inside the USSR.

The true purpose of the base was so secret that the Americans didn’t even tell the Danish – who governed Greenland before it was granted autonomy in 1979.

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The facility was eventually abandoned due to instability under the ice sheet

If it had continued, the plan was to construct some 2,500 miles of tunnels, covering an area of 52,000 square miles – roughly three times the size of Denmark.

The plan was for the army to be able to move the missiles from launch site to launch site underground via the tunnels, so the Soviets could never be entirely sure where they were.

US officials originally estimated that the remains of the base would be entombed in ice after what was expected to be a build-up of snow on top.

But it recently emerged that climate change means the submerged city could be exposed within 75 years.

There are now fears that radioactive material, sewage, diesel and other waste that it was assumed would be locked up indefinitely in the ice could be leaked into the surrounding environment with no plan as to who is responsible.

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